Project Summary Epithelial barrier dysfunction contributes to the pathogenesis of infection, inflammation and injury. E-Cadherin, a component of epithelial adherens junctions, plays an essential role in maintaining epithelial barrier function. Cigarette smoke exposure has been reported to downregulate E-Cadherin expression in epithelial cells. However, molecular mechanisms of cigarette smoke-induced suppression of E-Cadherin expression and epithelial barrier dysfunction remain largely unknown. In this project, we will investigate the role of a histone methyltransferase, euchromatic histone-lysine N-methyltransferase 2 (EHMT2 or G9a), in cigarette smoke-induced E-cadherin downregulation and epithelial barrier dysfunction. EHMT2 specifically methylates Histone H3 at lysine 9 (H3K9). Methylation of H3K9 by EHMT2 regulates gene expression by silencing euchromatin. Our preliminary data demonstrate that EHMT2 expression is robustly up-regulated in cigarette smoke-exposed normal human bronchial epithelial cells (NHBEs). The up-regulation of EHMT2 is associated with high levels of H3K9 methylation and E-Cadherin downregulation. EHMT2 knockdown or selective inhibition was able to restore E-Cadherin expression in cigarette smoke-exposed NHBEs. Furthermore, in a mouse model of cigarette smoke exposure, lung EHMT2 expression and H3K9 methylation were increased, which was associated with E-cadherin downregulation and epithelial barrier disruption in lung tissues. In the proposed studies, we will test we will test the hypothesis that EHMT2 up-regulation by chronic tobacco smoke exposure leads to epigenetic suppression of E-Cadherin expression and epithelial barrier dysfunction. Our specific aims are: (1) To determine the role of EHMT2 in epigenetic suppression of E-Cadherin expression and epithelial barrier dysfunction in tobacco smoke-exposed human bronchial epithelial cells. (2) To explore therapeutic mechanisms of EHMT2 inhibition against tobacco smoke-induced epithelial barrier dysfunction in vivo. Our studies could reveal new therapeutic targets to treat environmental tobacco smoke-induced epithelial cell dysfunction.